The present invention relates to an inking unit for printing presses using a hard printing image carrier and high-viscosity printing inks, and more specially offset printing presses, having a fountain roller in an ink fountain, a form roller for inking a printing image carrier fixed to a cylinder, the form roller running with the same surface speed as the printing image carrier, and an ink drum for forwarding ink from the fountain roller to the form roller, the ink drum having a different diameter, and more specially a smaller diameter, than the form roller and being turned at a different surface speed than the surface speed of the fountain roller.
In printing presses of this general design the inking unit has the main purpose of offering the form roller system an even, thin film for the printing image carrier or plate to take up. Under normal conditions of operation however this film is only taken up by the printing areas of the plate, that is to say not completely and a relief-like ink film is kept on the form roller. A further important function is for this reason that of levelling and evening off this relief-like film which would otherwise be responsible for "ghosting". In the case of such ghosting, the printing areas of the plate are no longer inked fully all over so that the ink density on the material printed is not great enough. On using high-viscosity printing inks, as for example offset printing inks, a roller system with a great number of rollers is generally used in order to get a thin ink film or coating with the desired thickness, the great number of small rollers further making certain that the printing plate is equally inked so that ghosting is not possible. Furthermore in prior art inking units of this sort adjustment of the ink rate of the breadth of the machine (along the axis) is possible using finger screws so that the amount of ink put on is matched with the amount of ink taken up by the form roller system. Such prior art inking units are not only very complex and take up much space, but furthermore may only be run by fully trained pressmen, and even so ghosting may still be possible. For this reason scavenger rollers have been used on the form rollers for evening out the thickness of the ink film, such a design however being very complex and, again, taking up space which is needed for other purposes.
For making the structure simpler and less complex, while cutting down the amount of space needed, "short inking units" have been designed, the inking unit of German Offenlegungsschrift specification No. 2,916,048 being representative of this branch of printing press development.
In this respect the desired thickness of ink film on the form roller is to be produced by a pressman-controlled pressure between the rollers acting together, by using different speeds of such rollers, that is to say causing one roller to be turned at a different or relative speed in relation to the other roller, and furthermore by a great number of ink storing or conditioning rollers used with the form roller and the ink drum. The ink film thickness is furthermore to be produced and controlled by an oscillating motion of the ink drum.